2010 - California State University, Long Beach Department of ...

6
New Powder
X-ray Diffraction
Instrument
By Dr. Shahab Derakhshan
The new powder X-ray diffractometer
(XRD) in my research laboratory is a
valuable addition to the single crystal
X-ray machine in Dr. Xianhui Bu’s lab and
completes our instrumental needs for crystallography
tasks. When single crystals with
suitable sizes are not available, powder diffraction
techniques are unique tools for
crystal structure determination. In addition,
the XRD instrument enables us to confirm
the formation of desired phases, phase
homogeneity and, if present, the type of
side products in polycrystalline samples.
The Panalytical X’pert Pro Alpha1 system
is equipped with a state-of-the-art
X’Celerator ultrafast detector. The monochromatic
incident beam results in highresolution
diffraction patterns.
The XRD instrument is housed in MLSC
302 and will be available for all interested
faculty labs in our department. This will
particularly be beneficial for materials
research labs. In addition, researchers from
other departments such as Physics and
Astronomy, Geological Sciences, Chemical
Engineering, and Mechanical and Aerospace
Engineering will be able to use this instrument
in collaborative research projects.
The XRD system will also be employed
in CHEM 332: Inorganic Chemistry Laboratory
and CHEM 531: Advances in Inorganic
Chemistry. The students will get hands-on
experience in obtaining diffraction patterns
and in analyzing the diffraction data. This
will provide a great opportunity for our
students to understand both the principles
of diffraction techniques and their applications
in crystallographic structure
determination.
By Dr. Michael P. Schramm
Dr. Julius Rebek, Jr.
2009 Allergan Distinguished Lecturer
The Department of Chemistry and Biochemistry was privileged to host Dr. Julius Rebek, Jr., a
chemistry professor at The Scripps Research Institute and director of The Skaggs Institute for
Chemical Biology, as the 2009 Allergan Distinguished Lecturer. Dr. Rebek visited our department
on Nov. 18. He presented two riveting talks: one, a lecture for a general audience; and the other, a
technical seminar on the topic of molecular recognition and molecular self-assembly.
Dr. Rebek received his Ph.D. degree in 1970 from the Massachusetts
Institute of Technology, studying peptide chemistry with Dr. D.S.
Kemp. He was appointed director of The Skaggs Institute for Chemical
Biology in 1996 after academic appointments at UCLA, University of
Pittsburgh and MIT, where he was the Camille Dreyfus Professor of
Chemistry from 1991-96.
Dr. Rebek’s early work included development of the three-phase
test for reactive intermediates and invention of molecular cleft structures
for molecular recognition. He was a pioneer in developing the
first synthetic, self-replicating molecules (J. Am. Chem. Soc., 1990, 112,
1249-1250). He has received numerous prestigious awards, given scores of presentations under named
lectureships, is an editorial advisory board member for many high-impact publications and commercial
companies, and has authored over 425 publications.
Dr. Rebek continues to be a leader in the field of molecular recognition and self-assembly. In his
first lecture, “Molecular Assembly and Encapsulation,” he described some of his group’s first efforts to
develop molecules that assemble and encapsulate other molecules. In these complexes, new chemical
phenomena emerge. Using NMR spectroscopy as a tool, Dr. Rebek convincingly demonstrated the driving
force that dictates self-assembly: appropriate filling of space. Moreover, these new assemblies
allow for the study of chemical phenomena within the capsules with time scales from milliseconds to
hours that could not otherwise be observed in solution, where the lifetimes of the relevant species are
too short. The NMR data was quite cleverly used to develop a series of breathtaking animations that
Rebek played for the audience, giving his best description of the actual physical behavior based on
chemical observation.
A second—standing room only—technical lecture elaborated on “The Inner Space of Molecules,”
where themes from earlier in the day were revisited in depth and applied to assemblies of greater
complexity and assemblies in which more than one guest is encapsulated in larger capsules. In these
studies, several new forms of stereoisomerism emerge. Molecules held in new arrangements give new
and thought-provoking challenges to conventional definitions of isomers. Dr. Rebek then elaborated on
some unusual contortions that molecules undergo as they are “driven” to fill space inside cavitands
and capsules. A new expanded capsule emerges when a seam of spacers is introduced. This arrangement
allows a long alkyl chain to go from a compressed and coiled conformation to a more familiar
expanded zigzag conformation. This behavior mimics our everyday notion of the compression of a
spring, except now it is reduced to the molecular level. An encapsulation complex of anandamine is
shown below with two “seams” of spacer molecules that allow this lengthy molecule to fill the space
defined by the two capsule halves at the
end. Coiling and kinks of the guest
emerge with unfavorable energetic consequences;
in the end, the energetic
benefit of encapsulation wins!
Throughout the lectures, despite
the complex experiments required to prove the existence of such complexes, Dr. Rebek had a masterful
way of keeping the audience on the edge of their seats, awaiting the next detail, discovery or animation.
It was truly a privilege for the department to host Dr. Rebek as our 2009 Allergan Distinguished
Lecturer. We are very grateful to The Allergan Foundation for their ongoing support of this program.